In secondary battery charging and discharging operations, the impedance of the secondary battery increases in a low-temperature environment, so electric power or an energy amount that can be charged and discharged at normal temperature cannot be obtained in a low-temperature environment. To solve this problem, a method of raising the temperature of a secondary battery by using a heater installed outside the battery is adopted. However, the heater produces a power loss, and it is impossible to evenly raise the temperature within a short time outside and inside the secondary battery.